1. Field of the Invention
The present invention relates to a photoresist composition comprising an amphoteric compound and a method for using the same. In particular, the present invention relates to a photoresist composition which is useful in a Top-surface Imaging Process by Silylation (xe2x80x9cTIPSxe2x80x9d) and a process for using the same.
2. Description of the Background Art
Thin layer imaging technologies such as TIPS are effective patterning processes for photolithography using a wavelength below 193 nm and optical lithography using an extreme ultraviolet (EUV) wavelength (e.g., 13 nm).
Some of the known limitations of the photolithography include substrate""s influence on the light (e.g., reflection, scattering, defraction, etc.), notching, standing wave effect, pattern collapse, non-uniformity of a critical dimension (CD), isolated and grouped bias (IG bias) and the like. In TIPS, a shallow exposure is performed which forms a latent image by diffusion of acids that is generated in the exposed region. The exposed region is then selectively silylated with a silylating agent. The silylated region serves as a mask, and the non-silylated region is dry-etched by O2 plasma (see FIG. 1). Thus, TIPS requires photoresist compositions having a high energy absorption coefficient and process conditions that have high selectivity in etching non-silylated regions during O2 plasma treatment.
TIPS is rarely influenced by substrates and topology. In addition, TIPS is less sensitive to transparency, adhesiveness and etching selection ratio of the photoresist composition. TIPS also has a much wider depth of focus in high resolution than a single layer resist (SLR). Thus, in some aspects, TIPS has more advantages than a general resist patterning process.
In addition, compared with a wet development of SLR, the dry development process of TIPS can be applied to a thick resist process in a high aspect ratio without causing a pattern to collapse. This advantage is useful on a substrate having a relatively low etching selection ratio, such as an oxide or metal. As a result, TIPS is recognized as an alternative to SLR.
In one particular example of TIPS, Plasmask 305-u (Japanese Synthetic Rubber) photoresist composition is used in KrF lithography. The incident radiation creates silylation sites on the top surface of the photoresist film. The exposed regions are then silylated by contating with a highly reactive gas phase silylation agent (e.g., an amino silane). An etching mask layer of silicon dioxide is then created by an oxygen plasma treatment. A photoresist pattern having a negative tone is then created using a dry development process.
To create a high resolution photoresist pattern requires a short wavelength in lithography process. It is believed that TIPS is well suited for such a high resolution photoresist pattern formation, in particular in a semiconductor device manufacturing process. Generally, however, current TIPS can not be used in a high resolution photoresist pattern formation. For example, in most cases roughness is generated at the edge of the resist pattern after dry development in TIPS, and therefore using a photoresist composition having high photosensitivity is not sufficient to create a useful pohtoresist pattern. Especially, since the line edge roughness (xe2x80x9cLERxe2x80x9d) generated during TIPS is often transferred to the underlying substrate during a pattern transfer step. This disadvantage of LER gets worse when the critical dimension (CD) is below 180 nm. FIG. 2 shows the LER generated using 180 nm wavelength lithography in the conventional SLR process and the TIPS. As shown in FIG. 2, the LER is more pronounced in the TIPS than in the SLR process. In general, the LER becomes more pronounced and more problematic as the pattern resolution increases (i.e., smaller the pattern size). For example, FIG. 3 shows a 120 nm L/S pattern obtained by the ArF TIPS. As is evident from FIG. 3, the LER must be improved significantly in order to be useful in a semiconductor device manufacturing process.
A line width variation resulting from the LER decreases the CD tolerance budget and the process margin. These decreases deteriorate process uniformity and device performance.
LER in the silylated resist pattern formation process is caused by various factors. Without being bound by any theory, it is believed that the LER is mainly due to the breakdown of edges of a silicon dioxide mask during the dry development process. In an ideal process, LER is not generated as depicted in FIG. 4A. However, as illustrated in FIG. 4B, it is believed that the gas phase silylation agent swells into the adjacent area of the exposed portion resulting in silylation of undesired regions and a low surface of the non-exposed section. It is believed that the LER occurs during the dry development process due to breakdown of these silicon dioxide layer that was formed in undesired regions and the unexposed regions in the silylation step.
Some of the significant problems of LER are a low silylation contrast, low silicon content, and silylation angle of the resist. It is believed that the silicon content of the etching mask has a significant affect on the generation of LER. In addition, LER can also occur due to the etching process, etching chemistry, etching selection ratio, mask etching, and etching profile such as sidewall morphology.
An object of the present invention is to provide a photoresist composition for a top-surface imaging process by silylation (TIPS) which can reduce line edge roughness (LER), and a method for using the same.
Another object of the present invention is to provide a semiconductor element produced by using the TIPS described above.